Physiological and behavioural measures of stress in domestic horses

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The welfare of domestic horses has been scrutinised by the scientific community in recent years. Traditional riding and stable management practices have been recognised to be at odds with the physical and behavioural adaptations of the horse. There is, therefore, a growing need to understand how modern horse management can impact on horse welfare. The first study in this thesis assessed the impact of common management practices on physiological stress in the horse. Faecal cortisol was higher in horses that were stabled and exercised, than turned out to grass with no exercise. The effect of exercise alone was also seen to increase levels of salivary cortisol. No change was seen in cortisol following short-term routine husbandry procedures such as exposure to the sound of electric coat clippers, but it was suggested that this required further investigation. The study confirmed exercise increased stress as reflected by cortisol concentration, and indicated that individual stabling may also contribute to elevated stress. The study recommended that horses may benefit from periods of rest and turn out to grass, to reduce stress levels and improve welfare. The measurement of stress for the purpose of welfare assessment is, however, best carried out using an integration of both physiological and behavioural measures. Behaviour scores offer non-invasive, quick and easy methods of assessing stress in domestic animals, but have typically been developed using only behavioural assessment of the stress response. In the second study a scale of behavioural indicators of stress was developed using behavioural and physiological measures for the purpose of assessing stress in stabled domestic horses. Principal component analysis of behavioural reactions and changes in salivary cortisol concentration in response to routine husbandry procedures, revealed three meaningful components that were used as the basis to the stress scale. Behavioural reactions to the husbandry procedures were further analysed by a panel of equestrian professionals using free choice profiling, and results were added to the appropriate components. The final scale comprised of four levels of stress (no stress, low, iii medium and high stress), and each category was further sub-divided into behaviour scores (BS). The scores represented accumulating levels of behavioural indicators of stress within each stress level, and provided indices of physiological stress. The scale offers an easy to use method of welfare assessment in horses, and reduces the need for additional physiological measures to be taken. The scale represented a novel approach to measuring stress, and was used in the final study to measure stress in horses stabled individually, group housed, and in horses moved from stabling to group housing. The effectiveness of the scale at measuring stress, was compared to the effectiveness of measures of heart rate variability (HRV) and faecal cortisol at measuring stress in the same horses. Lower levels of stress were recorded in group housed horses as measured by the BS, but measures of HRV and faecal cortisol showed no difference between those stabled or group housed. Stress levels were unaffected by the move to group housing, but BS declined significantly over the three weeks that the horses remained group housed. The physiological measures did not, however, reflect such a decrease in stress. Stress levels were also compared between horses housed in both environments whilst waiting to be fed. Group housed horses had lower stress levels as measured by the BS. Results provided by the BS were supported by relevant literature, and the scale appeared to be more sensitive than the physiological measures which did not yield significant results with the small sample sizes used in the study. The research confirmed short-term management practices horses are typically exposed to daily, can elevate their stress levels. Further research into which practices put horse welfare at a particular risk, and thus require modification or need to be avoided where possible, is necessary. The findings also suggest horse-owners may need to pay more attention to their horse’s stress levels, to avoid repeated or on-going stress that can jeopardise health and welfare. The scale of behavioural indicators of stress would provide a suitable method by which stress could be monitored and thus become a part of horse management.

Citation

Young, T. (2011). Physiological and behavioural measures of stress in domestic horses. (Doctoral dissertation). University of Liverpool, United Kingdom.

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